128 



COMPETITION AND CONSTANCY. 



The only bees able to carry a pollen load amounting to approximately 

 half of their own weight were species of Bombus; Apis, Colletes, Halictus, 

 and Prosopis coming next with a load a third of their body-weight. 



Table 88. — Summary. 



CONSTANCY. 

 Definitions. — Loew (1884) employed the term monotropic to designate 

 those apids that visit flowers of a single species, oligotropic for those visit- 

 ing only a few allied species, and polytropic for those that go indifferently 

 to very diverse flowers. Robertson further restricted the terms, designat- 

 ing as oligotropic only those bees the females of which collect pollen 

 from a single species or from those of the same genus or family and as 

 polytropic those that secure pollen from flowers of different families. 

 Following the English naturalists, Plateau (1901) denoted by constancy 

 the behavior of a polytropic hymenopter such as the honey-bee, which 

 visits various species of flowers during the season, but limits its activity 



